Conventionally, in the field of an actuator controller system having a multi-degree-of-freedom in rotation, which is used for controlling orientation of a monitoring camera and for a joint mechanism of a robot, there has widely been used an actuator mechanism or a motor system with a configuration in which a plurality of single-degree-of-freedom type motors are serially stacked in multistage. From a viewpoint of a reduction in a size and an enhancement in accuracy, in some cases, there is employed a multi-degree-of-freedom type actuator mechanism or a multi-degree-of-freedom type motor system which has a support system using a gimbal mechanism or a joint mechanism and an actuator system using an electromagnetic motor provided separately form the support system. However, in a conventional actuator mechanism or motor system, the serial multistage stacking structure of the single-degree-of-freedom type motors serves as a basic configuration irrespective of the presence of the gimbal mechanism or the joint mechanism. Therefore, the conventional actuator controller system has a difficulty in simplifying its configuration. For example, although a motor in an uppermost stage can easily be moved, a motor in a lowermost stage is moved with difficulties due to a load applied thereon. Moreover, the reduction in the size of the apparatus is limited by the aforementioned configuration. For this reason, an actuator mechanism or a motor system which is to be used for the conventional actuator controller system cannot always satisfy the required design.
In consideration of the situation, in recent years, attention has been given to the research and development of a spherical piezoelectric motor using a piezoelectric element as an actuator for driving a spherical driven member. In particular, the piezoelectric motor that drives a sphere as a driven member by a frictional force using a piezoelectric unit has been expected as a spherical motor of a next generation having small-size and high accuracy. However, it is difficult in the spherical piezoelectric motor to detect rotating positions in horizontal and vertical planes of the driven member with a high resolution, and a large number of axes that need to be controlled are provided. For example, in the case in which a spherical piezoelectric motor is used in a monitoring camera which is necessary and sufficient for a biaxial control of an elevation angle and an azimuth, a uniaxial control is further required for compensating for a shift around a radial axis of the camera.
Therefore, there has been known an actuator mechanism employing a gimbal mechanism and having such a structure as to include a three-dimensional piezoelectric unit and the gimbal mechanism. For example, there has been proposed a digital camera for controlling a posture of an imaging unit supported to be vertically and transversely rotatable with respect to a direction of a front of a camera body. An example of such digital camera is disclosed in JP-A-200-059674. The digital camera has an actuator member that abuts on a semispherical surface of a unit body of the imaging unit, and a piezoelectric element is placed to four side surfaces of the actuator member. And, a stacking type piezoelectric element and an abutting piece are placed to an upper end face of the actuator member. A protrusion formed on the abutting piece abuts on the semispherical surface of the unit body so that the actuator member directly rotates and drives the unit body in each of the vertical and transverse directions.
However, the gimbal mechanism generally has a shaft misalignment caused by a manufacturing process or an assembling process. In a driven member having a spherical shape, particularly, the processing of a rotating bearing portion is difficult to perform and there is a tendency that the shaft alignment is apt to be generated. An actuating displacement of the piezoelectric element is very small and a frictional contact state of the driven member and the piezoelectric unit greatly varies by the influence of the shaft misalignment. As a result, the actuator characteristic of the piezoelectric motor becomes unstable in some cases.
Generally, an amount of the shaft misalignment is several tens of micrometers and a displacement of expansion and contraction of the piezoelectric element is several micrometers. Therefore, idle rotation is generated over the piezoelectric element due to the assembling error and the contact state becomes unstable so that there is a possibility that a characteristic to be expected might not be exhibited. In the case in which a driven surface takes a spherical surface, high accuracy in a processing is required for fabricating the gimbal mechanism in such a manner that two shaft centers are orthogonal to each other. In the case in which an actuator mechanism such as a motor is stacked to assemble the gimbal mechanism, high accuracy in an assembly is required in a biaxial direction for a degree of parallelism and an interval of the actuator mechanisms in upper and lower stages.